Field of the Invention
The invention relates to a method for determining the position of an armature that is associated with an electromechanical actuating drive. The actuating drive is associated with an actuator, which preferably has a gas inlet or outlet valve of an internal combustion engine as the actuating element.
A prior art actuator is described in German Published, Non-Prosecuted Patent Application DE 195 26 683 A1, corresponding to U.S. Pat. No. 5,691,680 to Schrey et al. The actuator has a gas inlet or outlet valve and an actuating drive. The actuating drive has two electromagnets, between which an armature plate can be moved, in each case against the force of a resetter or resetting means. The armature plate can be moved by switching off the coil current on the holding electromagnet, and switching on the coil current on the attracting electromagnet. The coil current of the respectively attracting electromagnet is kept constant throughout a predetermined time period by a predetermined attraction value, and is then controlled to a holding value by a two-point regulator with hysteresis.
In order to determine the position of the armature plate, European Patent Application EP 0 493 634 A1, corresponding to U.S. Pat. No. 5,072,700 to Kawamura, discloses an optical sensor disposed in the electromagnet that detects the position of the armature plate. However, such a sensor requires space, which is available only to a very restricted extent, and requires costly wiring.
German Published, Non-Prosecuted Patent Application DE 195 44 207 A1 discloses measuring the magnetic flux that produces the magnetic force and the current through the field winding of an electromagnetic actuator to determine an armature movement. The movement variables including the armature movement, the armature speed, and/or the armature acceleration are calculated based on matched physical equations from the magnetic flux and from the current through the field winding, and are used as control variables for controlling the movement of the armature. However, Application DE 195 44 207 A1 contains no information on how the resistance of the field winding can be determined reliably for such a purpose.
It is accordingly an object of the invention to provide a method for determining the position of an armature that overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and that provides a simple and reliable method for determining the position of an armature.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for determining the position of an armature associated with an electromechanical actuating drive, the actuating drive having a first contact surface, at least one electromagnet with a coil and a second contact surface, the armature having an armature plate movably disposed between the first contact surface and the second contact surface, the method including the steps of determining a mean value of a measured voltage drop across a coil in an operating state in which a substantially constant current is flowing through the coil, determining a resistance of the coil as a function of the mean value of the measured voltage drop and the current through the coil, determining an inductive voltage drop across the coil from a difference between the measured voltage drop across the coil minus a voltage drop obtained by multiplication of the resistance of the coil by the current through the coil, determining a magnetic flux by integration of the inductive voltage drop across the coil, and determining a position of an armature as a function of the magnetic flux and the current through the coil.
In accordance with another mode of the invention, the mean value of the measured voltage drop across the coil is determined when a ratio of a change in a position to the position is less than a predetermined threshold value throughout a predetermined measurement time period.
In accordance with a concomitant mode of the invention, the mean value of the measured voltage drop across the coil is determined when a ratio of a distance between the armature plate and the second contact surface to a distance between the first contact surface and the second contact surface is greater than a predetermined threshold value throughout a predetermined measurement time period.
In a magnetic circuit that is formed by a coil, a core, an armature plate, and the air gap between the armature plate and the core, and provided the stray flux is negligible and the magnetic circuit is not saturated, the magnetic flux depends only on the current through the coil, and on the position of the armature plate. The magnetic flux "PHgr" is represented by the equation:                               Φ          =                                    1              N                        ⁢                                          ∫                0                            ⁢                                                                    U                    L                                    ⁡                                      (                    τ                    )                                                  ⁢                                  ⅆ                  τ                                                                    ,                            (        1        )            
where UL is the inductive voltage drop across the coil, which is advantageously given by the difference between the measured voltage drop across the coil minus the voltage drop that is obtained by multiplication of the resistance of the coil by the current through the coil.
The magnetic flux "PHgr" is represented by the equation:                               Φ          =                                    N              ·                              I                s                                                                    1                                  μ                  0                                            ·                                                2                  ⁢                                      (                                          s                      -                      K                                        )                                                  A                                                    ,                            (        2        )            
where:
A is the contact surface area of the core of the electromagnet with which the armature plate makes contact;
N is the number of turns on the coil;
IS is the current through the coil;
s is the position of the armature plate;
xcexco is the permeability of air; and
K is a constant. The position s is equal to the sum of the constant K and the length of the air gap between the armature plate and the core.
Equating equations (1) and (2) and solving for the position s produces the equation:                     s        =                                                                              μ                  0                                ⁢                                  AN                  2                                            2                        ·                                          I                s                                                              ∫                  0                                ⁢                                                                            U                      L                                        ⁡                                          (                      τ                      )                                                        ⁢                                      ⅆ                    τ                                                                                +          K                                    (        3        )            
If equation (1) is substituted in equation (3), the resulting equation is:                     s        =                                                                              μ                  0                                ⁢                AN                                            2                ⁢                Φ                                      ·                          I              s                                +          K                                    (        4        )            
Equation (4) allows the position of the armature plate to be determined, as a function of the magnetic flux and the current through the coil, in a simple manner.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for determining the position of an armature, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.